Neo-acids, including trialkylacetic acids, are generally carboxylic acids having at least one carboxyl group and at least one carbon connected directly to four other carbon atoms. Salts and other derivatives of neo-acids generally are very stable due primarily to the steric hindrance provided by their molecular structure. In particular, the alkyl groups on the alpha substituted carbon atom create a steric effect and hinder the ability of the neo-acid or its derivative to react. As a result, neo-acids or their derivatives have broad industrial applications, such as, for example, polymers and polymer additives, pharmaceuticals, agricultural chemicals and herbicides/pesticides, cosmetics, metal working and metal extraction fluids, vinyl chemical manufacturing, catalysts carriers and catalyst additives, aroma chemicals, fuels, lubricants, adhesives, transmission fluids, hydraulic fluids, tire manufacturing, electrical and electronic applications, etc. Common derivatives of neo-acids include acid chlorides, peroxyesters, metal salts, vinyl esters, and glycidyl esters.
Two industrial processes have been used to produce neo-acids on a large commercial scale. The first is commonly referred to as Shell's versatic acid process and the second as the Exxon process. Schematics and descriptions of each production process may be found in Carboxylic Acids (Trialkylacetic Acids), Johnson et al., Kirk-Othmer Encyclopedia of Chemical Technology Fourth Ed., Vol. No. 5, pages 192-206. In particular, the Exxon process may generally include reaction, degassing, catalyst recovery, and fractionation. Both processes use, as starting materials, olefins, carbon monoxide (CO), and acid catalysts in continuous stirred tank reactors to produce carboxylic acids. Typical reactions conditions include 40 to 100° C. and 70 to 100 bar carbon monoxide pressure with H3PO4/BF3/H2O in the ratio of 1:1:1 (Shell) or BF3.2H2O (Exxon).
Background references include U.S. Pat. Nos. 3,061,621; 3,068,256; 3,349,107; 3,527,779; 4,256,913; 4,311,851; 4,518,798; 5,241,112; 6,677,481; 6,717,010; 6,881,859; 6,919,474; U.S. Patent Application Publication No. 2005/0197507; GB 1,167,116; GB 1,174,209; and EP 0 590 087 B.
Due to the catalysts employed, a series of washing steps and settling drums are generally used primarily to recover and recycle catalyst and secondarily to remove metals and other catalysts components, such as, for example, residual salts and corrosion byproducts, from the crude carboxylic acid reactor effluent. Despite satisfactory approaches of the past, improvements in the removal of these materials remain highly desirable.